Stabilization of filament supply voltage



May 12, 1953 H. L. SCHULTZ 2,638,571

STABILIZATION OF FILAMENT SUPPLY VOLTAGE Filed Sept. 14, 1945 2o 24 FIG-l 23 l 7 2s 34- LOAD 31 32 AMPLIFIER FILTER RECTIFIER FIGZ 7O 24) HI 26 RECTIFIER FIGS 20' 24 T RECTIFIER INVENTOR HOWARD L SCHULTZ ATTORNEY Patented May 12, 1953 STABILIZATION OF FILAMENT SUPPLY VOLTAGE Howard L. Schultz, Wellesley, Mass., assignor, by mesne assignments, to the United States of America as represented by the Secretary of the Navy Application September 14, 1945, Serial No. 616,392

3 Claims. (01. 32366) This invention relates to an electrical system for stabilizing the alternating current voltage applied to a load irrespective of fluctuations of voltage as received from the source. This invention has been found to have particularly useful application when applied to control the voltage impressed upon the heaters of vacuum tubes, and especially to tubes such as the GL series which are used to operate as transmitting oscillators and therefore require exceptionally constant filament excitation.

Present practice of obtaining voltage stabilization of heater filaments is'to connect a ballast device in series with the supply circuit. This ballast device is commonly a small iron filament having the characteristic of providing greater resistance as the load tends to draw excessive current due to an increase in the transformer output voltages. This ballast device has proved to be unsatisfactory both because its characteristic of providing increased resistance as current flow increases is not ideal, and because the filament is not well adapted for resisting shocks. It has been found that use of the iron ballast filament has resulted in a large percentage of breakage thereof, especially where such filaments have been employed in connection with airborne radio mechanism.

It is an object of this invention to provide an electrical system for supplying a constant voltage to an electrical load irrespective of fluctuations of the voltage as supplied to the system.

A further object of this invention is to provide a method of producing stabilization of an alternating current power supply to an electrical load by automatically inserting a varying amount of impedance in series with the leads feeding the load, wherein the value of the impedance inserted is automatically determined by variation of the voltage across the load.

A more particular object of this invention is to provide stabilization of an alternating current power supply impressed upon the heater of a vacuum tube irrespective of voltage fluctuation of the power supply as received from the source.

Further objects and advantages of this invention, as well as its construction, arrangement and operation, will be apparent from the following description and claims in connection with the accompanying drawings, in which:

Fig. 1 is a circuit diagram illustrating a method of producing stabilization of an alternating current voltage applied to an electrical load irrespective of fluctuations of the voltage as received from the source;

embodying the principles of the invention disclosed in Fig. 1;

Fig. 3 illustrates a more simple circuit embodying the principles of the invention, this circuit being similar to but more specific than the system as disclosed in Fig. 1.

Referring to the drawings, Fig. 1 illustrates a circuit diagram providing for filament voltage stabilization under conditions in which the load may tend to draw excessive current due to an increase in transformer output voltage. An input transformer 20 having primary and secondary windings 2| and '22 respectively, is shown electrically connected to a load 23 by means of leads 24 and 25. Load 23 may be the heater filament of one or a series of vacuum tubes in which it is desirable to keep the voltage impressed on the filaments a constant value. Inserted in series with lead 25 is a primary winding 28 of a transformer 21 which may be a 6.3 volt conventional transformer. Secondary winding 28 of transformer 21 is connected across a plate 29 and a cathode 30 of a vacuum tube 3| having a control grid 32. Grid 32 is connected to lead 25 through a conventional amplifier, filter, and rectifier 35, 36 and 3'! respectively, in series, by a lead 33. Plate 29, cathode 30 and secondary winding 28 are joined to lead 24 through the above-mentioned amplifier, filter and rectifier by means of a lead 34. A potentiometer 35 is attached across leads 33 and 34 in order to set and adjust the operation of tube 3| at any desired level of operation.

In operation, the system shown in Fig. 1 is operative to regulate the bias of control grid 32 of tube 3| in a controlled amount, thereby varying the impedance which secondary winding 28 and consequently primary winding 26 of transformer '21 present. For example, if secondary winding 28 of transformer 21 is opencircuited, winding 26 will have a maximum reactance and the voltage appearing across load 23 will be a minimum. On the other hand, when winding 28 is short circuited, winding 26 will present a minimum reactance and the voltage appearing across load 23 will be a maximum. Intermediate values are obtained by adjusting the bias on control grid 32, which is done automatically by rectifying, filtering, and amplifying the voltage appearing across the load terminals and applying a portion of the direct current voltage to this control grid. As the voltage across the load 23 tends to increase, the voltage at grid 32 of tube 3| will go further negative thereby making tube 3| less conductive and caus- Fig. 2 illustrates a modified-form of a circuit '65 in: an increasein impedance presented by secvoltage fluctuations received from transform- Fig. 2 illustrates a modified form of the cir- Y cult of Fig. 1 in which input transformerlil,

load 23, leads '24 and 25, and transformer 21 are all common to those of Fig. 1. Fig. 2, a rectifier 38 is connected across the primary winding 2| of transformer vzil'throughleads 39 and 4!]. A standard voltage regulator tube 4| is connected in series with a .resistance 42 across leads 39 and 4!]. A triode tube '43 is pro- As shown 7 vided having its cathode 44 electrically conof tube 5B being joined to lead to by .means of a lead 5,2 and-across leads so and 439 through a condenser .53. Plate 5d of, tube 5!! is electrically connected to lead 52 through secondary windings 2 .8 of transformer 2'1, while the control grid -55 of tube 58 is connected to resistance 4.6 through a. lead 56 as shown. It will be readily understood that tube 43 is used as an amplifier to provide more sensitive control of the grid of tube 56.

In operation, assuming an increase .in voltage across leads it and it, the voltage impressed on. cathode M, of tube iil will remain substantlally constant with respect to lead 3.9 due to the regulatory action of voltage regulator tube M- At the same time, however, the voltage at control grid 48 oftube liwill increase with. respect to lead as with a resultant increase in electrical conductivity of tube til. As tube to becomes more and, more conductive, flow of current through resistor is simultaneously increased and the voltage at cathode iii 02 tube til rises with respect to the voltage atcontrol grid 55 thereof. It will readily be understood that as control grid 55 becomes more and, morenegative with respect to cathode 5i 1e icond-uctiuity. of

tube or will decrease, with a resultant decrease in flow of current through winding 280i transifiormer 2i, and a consequent increase .in impedance presented by winding 253. In this manner, voltage across the load 2.3 which may be .a heater filament of, a vacuum tube will be maintained constant irrespective of fluctuation in voltage from the source of power.

Fig. '3 presents .arnoresirnple arrangement than that of Fig. 2 and one similar to but morespecific than that of Fig. -1. In this embodiment of the invention no amplifier is included andericeptior the amplifying stage of Figs. 1 and 2, operation of the circuit of Fig. 3 takes place in asimilar manner tothat disclosed in connectionwith Figs. 1 and 2. .As shown, input transformer 26, leads .24 and 25, load 23, transformer 23, rectifier .33 and leads 39 and 4t, voltage regulator tube M and resistance 42 are :all common to the corresponding parts of 2. Voltage regulator tube at and r sta ce it all? e e ea eees isd, 1 e:

4 ries across lines 39 and 40. A triode tube 51 is provided to control passage of current through secondary winding 28 of transformer 21 having the control grid 58 thereof electrically connected intermediate tube 4| and resistance :32. Plate .59 and cathode- 60 of tube 5 1 are electrically connecteditowinding. 28 of, transformer 2'1 and to a resistance 6| connecting leads 3% and to by a :slidable contact through a lead 82.

If we again assume an increase in voltage across lines as and, voltage regulator tube M will again be operative to maintain a substantially constant voltage on control grid 58 of tube 57. At the same time, however, an increased voltage be impressed upon cathode (ill of tube 51, the result being that control grid 58 becomes more negative with respect to cathode til and the conductivity of tube '51 is thereby reduced. Reduction in current flow through winding 23 of transformer 2i again results in an increase in impedance presented by winding '25, thereby maintaining the voltage across load 23 at a constant value irrespective of fluctuation oi": voltage as delivered to power transformer 2t.

It is .tobe understood that various modifications. andichangesmay bemade in this invention without departing from the spirit and scope thereof as .set forth...in the appended claims.

What is claimed is:

1. A voltage regulating system comprising, a source of alternating current potential, a load, a transformer having primary and secondary coils, :said source, said primary coil and said load bein connected in series circuit relationship, a rectifier circuit connected across said source, said rectifier circuit having first and secondoutput terminals, a first electron tube having at; least an; anode, a cathode and a control grid, ;ananode load resistor coupled between saidranodeof said first electron tube and said second terminal of said rectifier circuit, means connected at least to said cathode of said first electron tube and said first terminal of said rectifier circuit for :ma-intaining said. cathode at a fixed potential relative to said first terminal of said rectifier circuit, means coupled between said firstand-seco-nd.terminalsof said rectifier circuit and to said grid of said first electron tube for coupling to said grid a selected fraction of the signal appearing between said first and second terminals, a second electron tube having at least an anode, a cathode and a control grid, said anode of said second control grid being coupled to zoneend of said secondary coil, said cathode of" said second electron tube being coupled to the other'end of said secondary coil, and means coupling said grid and said cathode, respectively, of saidsecond electron tube to separate points on the anode load resistor of said first electron tube, whereby the signal appearing across said anode loadres'istor of said first electron tube is applied as the grid-cathode signal of said second electron tube, and whereby fluctuations in said source of alternating current potential cause "variations in the giid-to-cathode potential of said second triode tube thereby causing changes in the impedance presented by said primary coil in said series circuit.

'2. A voltage regulating system comprising, a source of alternating current potential, a load, a transformer having primary and secondary coils, said source, said primary coil and said load being connected in series circuit relationship, a rectifier circuit connected across said source, said. rectifier circuithaying first and second output terminals, a series connected voltage regulator tube and resistor connected between said first and second terminals, said resistor being connected to said second terminal, a first triode tube having the cathode thereof connected to the junction of said resistor and said voltage regulator tube, a first potentiometer connected between the anode of said first triode tube and said second terminal of said rectifier circuit, a second potentiometer connected between said first and second terminals of said rectifier, each of said first and second pctentiometers having movable taps, the movable tap of said second potentiometer being coupled to the grid of said first triode tube, a capacitor coupled between said grid of said first vacuum tube and said second terminal of said rectifier, a second triode tube having the anode thereof coupled to one end of said secondary coil and the cathode thereof coupled to the other end of said secondary coil and to said second terminal or" said rectifier means, and means coupling the movable tap of said first potentiometer to said grid whereby fluctuations in said source of alternating current potential cause variations in the grid-tocathode potential of said second triode tube thereby causing changes in the impedance presented by said primary coil in said series circuit.

3. A voltage regulating system comprising, a source of alternating current potential, a load, a transformer having primary and secondary coils, said source, said primary coil and said load being connected in series circuit relationship, a rectifier circuit connected across said source, a series connected voltage regulator tube and resistor connected across the output of said rectifier circuit, a, first triode tube having the cathode thereof connected to the junction of said resistor and said voltage regulator tube, a first potentiometer having one end thereof connected to the anode of said first triode tube, the other end of said first potentiometer being connected to the output terminal of said rectifier circuit, to which said resistor is connected, and to one end of said primary coil, a. second triode tube having the anode thereof connected to the other end of said primary coil, the cathode thereof also being connected to said one end of said secondary coil, a second potentiometer having one end thereof connected to said one end of said secondary coil, said voltage regulator tube and said first potentiometer, said first and second potentiometers each having movable taps, the movable tapof said first potentiometer providing grid bias to said second triode tube and the movable tap of said second potentiometer providing grid bias to said first triode tube, whereby fluctuations in said source of alternating current potential cause variation in the voltage applied to the grid of said first triode tube and in the voltage at the cathode of said second triode tube, ensuing changes in the conduction of said second triode tube causing changes in the impedance presented by said primary coil in said series circuit.

HOWARD L. SCHULTZ.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 2,054,496 Craig Sept. 15, 1936 2,392,434 Trucksess Jan. 8, 1946 2,403,424 Zuschlag July 2, 1946 2,444,472 Schooley July 6, 1948 FOREIGN PATENTS Number Country Date 441,704 Great Britain 1936 661,540 Germany June 21, 1933 

